Human rhinovirus VP4: membrane pore-forming capsid protein and conserved target for broadly neutralising antibodies

Human rhinovirus (HRV) infects humans more frequently than any other virus and is responsible for approximately 70% of all subclinical respiratory infections (the common cold) which costs the UK £billions every year. HRV infection is also associated with more serious clinical outcomes such as severe lower respiratory tract infections of infants and exacerbations of chronic lung diseases such as asthma.

Viruses must gain entry to host cells for infection to begin and the membrane of the cell presents a barrier which the virus must penetrate. For many viruses, the process by which this is achieved is not well understood. HRV is a very simple virus which makes a good model system for understanding this process in more detail. The virus comprises a single strand of RNA (the virus genome, the blueprint for making new virus) enclosed in a protein shell or capsid. Based on previous experiments we believe that during entry to the cell, a small internal capsid protein called VP4 is released from the virus to form a pore in the membrane through which the RNA is delivered into the cell.

The host immune response to a virus infection often produces antibodies which bind to the virus and bring the infection under control. Often a virus can circulate as several strains or types with variation in their outer surface such that antibodies will only recognise and provide protection against one specific virus type. In the case of HRV there are over 100 different types which is thought to explain why colds are so frequent and has limited the prospects of a vaccine. Unlike most of the capsid, the VP4 protein is highly conserved between HRV types and previous experiments showed that antibodies against VP4 can neutralise multiple types of HRV.

We will carry out studies to gain novel understanding of how VP4 forms the pore in the membrane, how it emerges from the particle and how antibodies against VP4 can have broadly neutralising activity against multiple types of the virus.

The picornavirus capsid comprises sixty copies of each of VP1, VP2, VP3 (which form the icosahedral non-enveloped particle) and VP4 which is a small, myristoylated internal protein which stabilises the capsid structure. During cell entry, VP4 is irreversibly externalised and interacts with membranes to form a multimeric pore thought to be involved in delivery of the RNA genome into the cell. In this project we will use virus particles, VP4 peptides, liposome model membranes and biochemical and structural approaches to gain fundamental understanding of how VP4 multimerises and inserts in the membrane and how VP4 emerges from the HRV capsid.

The capsid is dynamic and undergoes a process of 'breathing' whereby internal components such as the N-terminus of VP4 are transiently exposed at the capsid surface. Antibodies raised against N-terminal VP4 peptides can recognise VP4 and neutralise the virus. The N-terminus of VP4 is highly conserved and existing evidence from studies with HRV and related picornaviruses strongly suggests that antibodies against VP4 are highly likely to be broadly neutralising. We will define protective epitopes in VP4 and present them in an immunogenic form to induce antibodies that react with the emerging N-terminus of VP4, neutralise the virus and protect against infection in an established murine model for HRV infection.

The major outcome of this project will be improved scientific understanding of how viruses invade host cells and how such processes can be targeted by antibodies. In addition to this benefit to the academic scientific community, the nature of the proposed research may also contribute to strategies for novel vaccines which may lead to tangible benefits of a social and economic nature. These will be of benefit to the institutions and collaborators carrying out this work, and to the MRC and its stakeholders such as the UK Department of Health and equivalent organizations worldwide. In addition, the outcomes of the research will be of interest to other groups such as the World Health Organization and Global Poliovirus Eradication Initiative, general practitioners, healthcare workers, students and the general public. Engagement with these diverse groups will be achieved via meetings, articles in the trade press, tailored web pages, and press releases to the media.

The proposed studies may lead to new approaches for developing vaccines for non-enveloped viruses. In this case, additional funding will be sought from MRC and other sources for further development. There is extensive experience of patent applications, technology development and commercialization within Pirbright, Imperial and the partner institutions. Additionally the applicants have existing links with a number of pharmaceutical companies who may be interested in the outputs from this work. These links, and other informal contacts within the scientific community and the industry, will be used to explore avenues that will maximize the impact of this research.